Recently, various audio sources have been distributed and provided in the open market; and DVDs (digital versatile disks) store multi-channel audio signals of 5.1 channels, for example. Digital surround systems for reproducing audio sources have come to be widespread among general households. FIG. 14 is a plan view showing an example of a layout of speakers in a digital surround system, wherein reference numeral Zone designates a listening room for performing audio surround playback; reference numeral U designates a listening position; reference numeral SP-L designates a speaker for reproducing a main left signal L; reference numeral SP-R designates a speaker for reproducing a main right signal R; reference numeral SP-SL designates a speaker for reproducing a rear left signal SL; reference numeral SP-SR designates a speaker for reproducing a rear right signal SR; reference numeral SP-SW designates a sub-woofer for reproducing a sub-woofer signal (a low-frequency signal) LFE; and reference symbol MON designates a video device such as a television receiver.
The digital surround system of FIG. 14 can effectively produce various sound fields. Since plural speakers are separately arranged in the listening room Zone, the digital surround system has drawbacks in that in order to arrange surround rear speakers SP-SL and SP-SR in the rear of the listening position U, wiring lengths between the speakers must be increased, and the arrangement of the rear speakers SP-SL and SP-SR is limited by the shape of the listening room Zone and the arrangement of furniture.
In order to solve the aforementioned drawbacks, rear speakers are formed using directional speakers having sharp directivities and arranged in front of the listening position, while a sound reflection board is arranged in the rear of the listening position. There is provided an audio surround system in which surround-channel sounds emitted from directional speakers are reflected on sound reflection boards so as to demonstrate an effect similar to an effect realized by arranging rear speakers in the rear of the listening position. This is disclosed in Japanese Unexamined Patent Application Publication No. H06-178379, for example. FIG. 15 is a plan view showing an example of a layout of speakers in an audio surround system disclosed in this Japanese Unexamined Patent Application Publication, wherein reference numerals B-L and B-R designate sound reflection boards.
It is possible to use a method in which a wall surface positioned in the rear of a listening room is used as a sound reflection board as shown in FIG. 16. In a three-dimensional stereo audio playback method disclosed in Japanese Unexamined Application Publication No. H03-159500, for example, an array speaker is used to produce virtual sound sources in the space. By use of this technology, it is possible to produce virtual speakers in the rear of a listening position.
As described above, it is possible to produce virtual speakers in the rear of a listening position by arranging sound reflection boards in the rear of the listening position or by using a wall surface of a listening room as a sound reflection board. However, this method may be strongly affected by sound directly emitted from a directional speaker arranged in front of the listening position; hence, it has a problem in that sound localization similar to sound localization realized by arranging rear speakers in the rear of the listening position cannot be affected. This is because human ears are shaped to easily pick up sound from the front, and the Haas effect may occur because direct sound reaches the ears of the listener first since a distance for directly transmitting sound to the listener without the intervention of a wall is shorter than a distance for transmitting sound emitted from a directional speaker after reflection on a wall.
This invention is made to solve the aforementioned problems; hence, it is an object of the invention to provide a directional speaker control system adapted to an audio surround system in which sound emitted from a directional speaker is reflected on a wall surface or a sound reflection board so as to produce virtual speakers, wherein good sound localization is realized by correcting the directivity of the directional speaker.